This invention relates generally, as indicated, to a fluid actuator especially of the type used to control the movements of flight control surfaces of military aircraft and the like. More particularly, the invention relates to the provision of a ballistically tolerant rod bland bearing for such actuator, to prevent the actuator from jamming in the event that the piston rod is hit by a ballistic projectile or the like.
Should a ballistic projectile such as a bullet or shrapnel hit the actuator piston rod, it will destroy the precision ground sealing surface thereon and produce petals of metal or large burrs which will cause the piston rod to jam in the rod gland and freeze the actuator against movement.
If the raised petal or other such abutment on the rod (hereafter referred to as a rod deformation) is not too large, this type of actuator jam can be reduced or eliminated by fabricating the rod gland out of a frangible material which permits portions of the rod gland to break off when forcibly contacted by the rod deformation, thus continued movement of the rod deformation past the rod gland. To prevent failure of the rod gland due to normal burst and fatigue requirements, the rod gland must be able to withstand the usual internal actuator pressure loads but not the required maximum jam clearance load. In a conventional frangible gland design, these restrictions only allow the frangible rod gland to clear a relatively small deformation on the piston rod, thus making it unsuitable for larger rod deformations.
Heretofore, it was known that larger rod deformations could be cleared utilizing frangible sections or a frangible pin to retain the rod glands in place during normal operation but which will rupture or break in response to an axial inward jam clearance force applied thereto. However, such rod glands were normally supported so that the frangible means would not break when relatively high axial outward forces are applied to it, making it unsuitable for applications in which the actuator is susceptible to rod damage interiorly of the actuator. Also, there is a continuing need for more simplified rod gland designs including a rod gland bearing which will separate from the rod gland in response to a jam clearance force being applied to the rod gland bearing during movement of the piston rod in one or both directions to clear relatively large deformations of the piston rod either exteriorly or interiorly of the cylinder.